Field of the Invention
This invention pertains to the folding and unfolding of helicopter blades.
Description of the Prior Art
It is an accepted and necessary design feature of helicopters to have a large diameter swept area of the main rotor blades. This feature, however, causes significant space claim issues when the helicopter is not in use or needs to be transported long distances in transport aircraft or on the crowded deck of sea going vessels, which is often the case. To reduce the space claim of the helicopter to be stored or transported, the main rotor blades are either removed or folded so that the longitudinal axis of the blades are nearly parallel to the longitudinal axis of the fuselage of the helicopter.
To ensure that the balance of each rotor remains intact, it is not desirable to the operation of individual helicopters to have their main rotor blades removed at any time. Removing the blades from a host helicopter requires that the helicopter go through lengthy and complex rebalancing procedures before flying once again. It is therefore highly desirable to produce a main blade fold system that allows for retention of the blades with a minimum of effort and time and risk of damage to the host aircraft or the blades.
The main rotor blade folding procedures are designed so that each helicopter can have its blades completely folded and stored, locked on the fuselage without the aid of power tools or external lifting equipment. To facilitate this operation, a “blade fold kit” is provided to helicopter transport personnel that contain all the manual tools, fixtures and lifting devices to manually fold the blades and secure them to the host helicopter fuselage in a minimum of time with a minimum of effort. The same “blade fold kit” must be used to “unfold” the blades and restore the blades to their original flight position without damage, in the least amount of time possible.
Devices for the automatic folding, i.e., without manual intervention, of the main rotor blades of a helicopter are already known. These devices, powered by hydraulic, pneumatic and/or electrical automatic folding devices are quite complex and their extensive weight and complexity prevent them from being incorporated on a wide scale on lightweight civilian and military helicopters.
Devices permitting the manual folding of the main rotor blades of a helicopter, as described above, are also known. These manual “blade fold kits” are simpler and more reliable than automatic or semi-automatic folding devices. Because they are provided as “kits” to be used only when helicopter main rotor blades require folding or unfolding for storage or transport, no additional permanent weight is added to the helicopter.
Various such devices have been developed for folding the main rotor blades, specifically multi-blade helicopters with three or more blades, each blade of which necessarily comprises of a flapping hinge and a hinge for controlling the angle of incidence. These rotors have thus presented the necessity of locking the flapping hinge and the rotational hinge during transportation in order to prevent any movement of each of the main rotor blades about these hinges.
Devices describing manual blade folding devices for helicopters with three or more blades include U.S. Pat. No. 6,213,712, in which the inventor describes a device to control the pitch and flap angles of the main rotor blades, and further describes device features to enable the folding of the blades rearward without damage. In U.S. Pat. No. 6,860,450, in which the inventors describe a method for folding the blades of an Apache Helicopter (AH-64) which has four main rotor blades, similar features are disclosed. In both of these and other inventions, however, only passing reference is made to the removal of one or both of the flight blade pins at the pitch housing and connection point of the blade, and the attachment of a “pole” at or near the outboard end of each blade to control the position of the blade.
In practice, it has been discovered that the process of preparing the blades to be folded includes the removal of one flight blade pin and then removing the other during the process. Because the helicopter blades are not supported or controlled at or near the center of gravity for this operation, and only at the far end through the use of a “pole” attached to the outboard end of the blade and manually manipulated by two or more personnel, achieving balance enough to remove the forces present at the blade pins is very difficult and time consuming. This occurs not only during the fold process, but again at the unfold process when the transport blade pins are removed and replaced with the flight blade pins as the main rotor blades are returned to their proper flight ready position.
It is a common occurrence during a main rotor blade fold or main rotor blade unfold operation of the Apache Helicopter, for example, that as many as eleven people are required for the fold and unfold operations, and the time and effort required to manipulate the outward end of each main rotor blade correctly to achieve what is commonly known as the “sweet spot,” and at that moment relieving stress at the rotor blade pins sufficiently to remove the flight blade pin(s) is quite high and unacceptable.